1. Field of the Invention
This invention relates to compositions and methods for the treatment of pain and discomfort associated with sensitive teeth.
2. Description of Related Art
Stannous fluoride (SnF2), has been used in dentistry since the 1950""s to treat various oral conditions. Topical application of SnF2 consistently has shown dramatic reductions in dental caries activity with minimal side effect. SnF2 has also been indicated clinically to be efficacious in the reduction of dentinal hypersensitivity. This latter therapeutic effect is believe to be attributable, to a large degree, to the stannous ion (Sn2+) component of the salt.
U.S. Pat. No. 5,690,912 teaches that in order for the stannous ion to be efficacious in treating dentine hypersensitivity, it must be stable and freely available and not in chemical combination with other ingredients. The patent discloses oral hygiene preparations containing SnF2 in a composition with 87-97 wt. % anhydrous glycerine and 2-10 wt % polyethylene glycol having an average molecular weight of 1000.
Besides SnF2, other materials have been disclosed as active ingredients in the treatment of hypersensitive teeth. U.S. Pat. No. 3,863,006 discloses the use of potassium, sodium and lithium nitrates as desensitizing agents. U.S. Pat. No. 5,270,031 discloses the use of a water soluble or water swellable polyelectrolyte or partial salts thereof as a dental desensitization agent.
U.S. Pat. No. 5,693,314 teaches that attempts to include mixtures of a desensitizing agent such as SnF2 with another desensitizing source such as potassium salts, i.e., potassium nitrate, in a single dentifrice composition are of limited effect. Additionally, prolonged contact between Sn2+ and nitrate ion in a single dentifrice results in a reaction of these ions into potentially toxic materials. Thus, the solution is in keeping the two desensitizing sources separate from each other, and combining them for the first time only on the surface of the teeth, thus avoiding any appreciable formation of insoluble tin or reaction product of tin.
U.S. Pat. No. 5,932,192 restates earlier teachings that stannous compounds react with water and other common oral care ingredients to form insoluble tin. Further, stannous ions impart an astringent, bitter, sour metallic taste to dentifrices. The patent provides the same solution of a two-component composition of stannous salt and potassium salt, in which the water content within the potassium salt component is at least 44 wt. % and the overall water content is at least 22 wt. %, whereby the astringency, sourness and bitterness of the stannous salt is significantly reduced.
Applicants have found that there is no need to for dual component toothpastes with dual containers to keep the stannous fluoride compounds separate from other desensitizing agents in a desensitizing composition. We have surprisingly found that stannous fluoride as a desensitizing agent can be combined directly with another desensitizing agent in a dentifrice composition, without the cumbersome and costly manufacturing and packaging processes required in the prior art. In combining stannous fluoride directly with another desensitizing agent to further take advantage of the known anticaries and anti-microbial action of SnF2, we have also surprisingly improved the physical properties of a gel dentifrice composition in its appearance. The desensitizing composition of the present invention also surprisingly exhibits excellent organoleptic and flavor release properties.
The invention provides a desensitizing agent comprising an anhydrous system containing stannous fluoride and at least another desensitizing agent, a cross-linked water soluble or water swellable polyelectrolytes or a partial salts thereof.
The invention further provides a method for treating dentinal sensitivity by administering a composition comprising an anhydrous system containing stannous fluoride and at least another desensitizing agent, water soluble or water swellable polyelectrolytes or a partial salts thereof.
Besides the desensitizing agents, an essential component of the present invention is an orally acceptable dentifrice carrier. The carrier for the components of the present compositions can be any dentifrice vehicle suitable for use in the oral cavity. Such carriers include the usual components of toothpastes, creams, tooth powders, prophylaxis pastes, lozenges, gums, mouthwash concentrate and the like and are more fully described hereinafter. Toothpastes are the preferred systems.
First Desensitizing Componentxe2x80x94Stannous Fluoride
Stannous fluoride is used as one of the desensitizing agents in the present invention. It is available in a powder form. Generally, the stannous fluoride in the various preparations of the present invention is between about 0.10 to 2% by weight, and preferably about 0.3 to about 1% by weight.
Second Desensitizing Component.
The second synergistic desensitizing agent of the present invention is water soluble or water swellable and contains functional groups capable of bearing a charge. The water soluble or swellable polymers are generally called polyelectrolytes, that is, polymers which bear one or more functional groups capable of bearing a charge in an aqueous medium. These polyelectrolytes can be anionic, cationic or amphoteric.
One example of an anionic functional group is the carboxylate group. This group is found in such polymers as polyacrylic acid, copolymers of acrylic acid and maleic acid, copolymers of methacrylic acid and acrylic acid, copolymers of alkyl vinyl ethers and maleic acid or anhydride, and the like. In the alkyl vinyl ether/maleic acid or anhydride copolymers, the alkyl group generally contains 1 to about 10 carbon atoms and is most preferably a methyl group. The copolymer can be produced using procedures well known in the art or commercially available forms can be employed. Polyacrylic acid can be obtained from B. F. Goodrich under the tradename Carbopol(copyright) as a cross-linked polyacrylic acid. These and other usable anionic polyelectrolytes are available from various other manufacturers. Another anionic functional group is the sulfonate group which is found for instance in sodium polystyrene sulfonate polymers.
The polyelectrolytes can contain cationic functional groups such as quaternized amines, imines, amides and alkyl ammonium groups. Examples include copolymers of vinyl pyrrolidone and dialkyl aminoalkyl methacrylates, chitosan, cationic celluloses and the like. A copolymer of vinyl pyrrolidone and dialkyl aminoalkyl methacrylate is available from International Specialty Products under the tradename Gafquat(copyright).
Amphoteric polymers can also be used as a dentinal desensitizing agent. Examples include the aminoalkyl methacrylate and acrylates, copolymers of aminoalkyl acrylamides and acrylates, gelatin and the like.
The commercially available polymers are produced over a range of molecular weights. It is preferable to employ the highest molecular weight grade consistent with the viscosity of the formulation being prepared and concentration of the agent. A preferred polymer is a polyacrylic acid having a molecular weight of at least 500,000.
The second desensitizing agent can also be in the form of super-absorbent acrylic polymers, i.e., hydrogel forming polymers are water-absorbent, yet water-insoluble, cross-linked polymers that have been typically used in diapers, feminine hygiene articles and surgical dressings. Descriptions of super-absorbent polymers and their uses are found in U.S. Pat. Nos. 3,669,103 and 3,670,731. They are substantially water-insoluble, cross-linked, partially neutralized polymers, generally having a gel capacity of at least 50 grams of deionized water per gram at 20xc2x0 C. and often at least 100 grams, 200 or more grams of water per gram dry weight of polymer at 20xc2x0 C.
A preferred super-absorbent acrylic polymer is a water absorbent, water-insoluble, cross-linked acrylic polymer having a gel capacity of at least 50 grams deionized water per gram dry polymer at 20xc2x0 C. The most preferred polymer is a sodium polyacrylate emulsion polymer sold by Allied Colloids under the trade designation DP6-6984.
The formulations will contain a second desensitizing agent in an amount which is generally from about 0.1% to 20% by weight of the polymer or its partial salts, with about 0.5-10% being preferred and about 1-5% most preferred. For any given concentration, viscosity 9 generally increases with molecular weight and for any given molecular weight, viscosity generally increases with concentration.
Anhydrous Base Component
It is desirable to include humectant material in the dentifrice composition of the present invention to keep it from hardening. Suitable humectants include glycerin, sorbitol, and other edible polyhydric alcohols such as polyethylene glycol at a level of from about 15% to about 98 wt. %. The humectant can be a mixture of humectants, such as glycerol and polyethylene glycol of molecular weight in the range of 200-1000, but other mixtures of humectants and single humectants may also be employed.
Optional Components.
In the present invention, the second desensitizing agent water soluble or water swellable polyelectrolyte functions as a thickening agent. However, other thickeners may still be added to give the final product the desired consistency. Inorganic thickeners may include fumed silicas such as Cabosil available from Cabot Corporation, and thickening silicas including those available from Crosfield Chemicals designated Sorbosil TC-15 or Sylox 15 from W. R. Grace. Organic thickeners of natural and synthetic gums as colloids may also be incorporated in the dentifrice composition of the present invention in which potassium salts are an ingredient. Examples of such thickeners are carrageenan (Irish moss), xanthan gum and sodium carboxymethyl cellulose, starch, polyvinylpyrrolidone, hydroxyethylpropylcellulose, hydroxybutyl methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose.
Abrasives may be incorporated in the compositions of the present invention. Preferred abrasives are siliceous materials, such as silica, and will normally have a mean particle size up to about 10 microns and a very high surface area e.g. in the range of 150-750 square meters/gram. Besides silica, other abrasives may also be employed, including sodium metaphosphate, potassium metaphosphate, tricalcium phosphate, calcium phosphate dihydrate, anhydrous dicalcium phosphate, calcium pyrophosphate, magnesium orthophosphate, trimagnesium phosphate, calcium carbonate, sodium bicarbonate, alumina trihydrate, aluminum silicate, zirconium silicate, calcined alumina and bentonite.
Suitable preservatives in this invention include benzoic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), ascorbic acid, methyl paraben, propyl paraben, tocopherols and mixtures thereof.
Coloring agents in this invention are used in amounts effective to produce a dentifrice of the desired color. These coloring agents may be incorporated in amounts up to about 3% by weight of the dentifrice composition of the present invention. The coloring agents may also include natural food colors and dyes suitable for food, drug and cosmetic applications. A preferred opacifier, titanium dioxide, may be incorporated in amounts up to about 2.0 wt. %, preferably less than about 1.0% w/w of the composition.
The sweetener content will normally be that of an artificial or synthetic sweetener and the normal proportion thereof present will be in the range of 0.1 to 1% by weight, preferably 0.3 to 0.5% by weight. Anhydrous carbohydrate sweeteners include sorbitol, lycasin, and hydrogenated glucose syrup.
The flavors which may be used in the invention include natural and artificial flavors known in the dentifrice art. Suitable flavors include, but are not limited to, mints, such as peppermint, citrus flavors such as orange and lemon, artificial vanilla, cinnamon, various fruit flavors, and the like.
Preparation.
A dentifrice composition according to the present invention can be made by first combining the humectants, one or more sweeteners, flavors, and the desensitizing agents at a temperature sufficient to dissolve and mix all the components well, preferably from about 90xc2x0 to 140xc2x0 C. Abrasive, colors, flavors, and other optional components may be added and mixed in at the same time or subsequently in steps. A vacuum is pulled if necessary for deaeration.
The apparatus useful in accordance with the present invention comprises mixing apparatus well known in the dental art, and therefore the selection of the specific apparatus will be apparent to the artisan.